1. Field of the Invention
This invention relates to ceramic materials useful for ceramic tools comprising mainly alumina, and more particularly to improved ceramic materials which can be safely used for high-speed cutting.
2. Description of the Prior Art
The use of Al.sub.2 O.sub.3 in combination with small amounts of CaO, MgO and Y.sub.2 O.sub.3 has hitherto been known, and such compositions have widely been used for the production of abrasion resistant, dielectric and heat resistant porcelains. However, ceramic materials produced from such compositions, when used as cutting tools, have suffered from the disadvantage that they are liable to break, particularly in high-speed cutting applications, since parts of the cutting edge may rise in temperature to as high as 1,400.degree. C., resulting in mechanical stress and breakage. In the art of cutting, therefore, it has been difficult for such ceramic materials to find applications other than finish cutting.
To solve the problem as described above, improved ceramic materials have been proposed, including ceramic materials containing 10 to 30% carbides, (e.g., TiC) nitrides, and borides, and molding the resulting mixtures by a hot-press processing. Although these ceramic tools are durable for certain heavy-duty cutting, they are, when used in high-speed cutting, inferior in abrasion resistance, because of oxidation of the added carbides, nitrides, and borides.
Therefore, it has long been desired to obtain improved ceramic materials having improved high-speed cutting properties.